This change is to align the 5.5 performance_schema.THREADS
table definition with the 5.6 performance_schema.THREADS table,
to facilitate the 5.5 -> 5.6 migration later.

In the table performance_schema.THREADS:
- renamed ID to PROCESSLIST_ID, removed not null
- changed NAME from varchar(64) to varchar(128)
to match the columns definitions from 5.6

Adjusted the test cases accordingly.

Note: this fix is for 5.5 only, to null merge into 5.6